Hepcidin inhibits iron efflux from human intestinal Caco-2 cells

Hepcidin, a 25 amino acid produced by hepatocytes in response to iron loading and inflammation, is the main circulating iron regulatory hormone [1]. Hepcidin is predicted to exert its regulatory action by binding to the iron efflux protein ferroportin, inducing transporter degradation and thereby inhibiting iron release from cells [1]. Our work in macrophages supports this proposed mechanism for the action of hepcidin [2]. However, hepcidin does not alter ferroportin expression in intestinal epithelial cells [2,3], suggesting that they may be less responsive to hepcidin. To further test this hypothesis we measured changes in iron transport in Caco-2 cells exposed to hepcidin. Caco-2 cells were grown for 21 days on Transwell inserts. At the start of each experiment, 59FeCl3 (10μM) was added to the apical medium and hepcidin (1μM) was added to the basolateral medium. The cellular accumulation of iron and its release into the basolateral medium were measured over the following 24h by gamma counting. Data are presented as mean ± SEM, and were analysed using Student’s unpaired t-test with differences considered significant at P<0.05. Despite our previous observation that hepcidin does not alter ferroportin expression [2,3], iron efflux from Caco-2 cells into the basolateral medium was significantly decreased in hepcidin-treated cells (normalised data at 24h time-point; control, 1.00 ± 0.08; + hepcidin, 0.68 ± 0.05, P<0.004, n=11). This was associated with a significant increase in cellular iron accumulation after 24h (normalised data; control, 1.00 ± 0.04; + hepcidin, 1.58 ± 0.21, P<0.01, n=11). Our data support the notion that in intestinal epithelial cells, hepcidin can block iron release without inducing degradation of ferroportin. Together with our macrophage data, this suggests that the actions of hepcidin are cell-type specific.